The reticular formation, a group of nerve cells located in the central core of the brainstem, is important in the control of many bodily functions, e.g. of sleep, alertness, respiration, blood pressure, and pain. Clinically, it has been implicated in coma, sleep disorders, motor disorders, and epilepsy. Previous work in this lab has demonstrated that the reticular formation of reptiles (snakes, lizards, turtles, and crocodiles) is anatomically quite similar to that of mammals, including humans. But small differences were found which suggest how different parts of the reticular formation may have evolved. Recent evidence from this lab has uncovered possible differences in the relationship of the reticular formation with the forebrain in elasmobranch fishes. Our hypothesis is that the reticular formation of all vertebrates is organized similarly, but some parts of it may be evolutionarily much older than others. Primitive vertebrates -and their brains- represent an early stage of vertebrate evolution and so can help us understand how the reticular formation first began. This project will focus on three species of primitive vertebrates, all elasmobranch fishes: the horned shark, the thornback guitarfish and the freshwater stingray. A new retrograde tracer, Fluoro- Gold, will be used to identify reticular groups which project to the spinal cord or the forebrain and to delineate the denroarchitecture of the cells. Immunohistochemistry will be used to identify cell groups which contain serotonin, enkephalin, or tyrosine hydroxylase. Combined, these techniques will allow us to find cells projecting to the spinal cord or the forebrain and containing particular transmitter systems. These tools will give us very powerful means of comparing elasmobranch reticular cells with mammalian ones. Information forthcoming from this research will help us better understand what are the most basic and widespread features of the reticular formation. This is of fundamental importance to understanding how the reticular formation controls vital bodily functions in humans and thus how it might be implicated when these vital functions are disturbed from disease of injury.